This invention relates to electrolytic cells and more particularly to the effective sealing of such cells.
Electrolytic processes are well known in many industrial branches of electro-chemistry. In the chlor-alkali industry, for example, electrolytic processes used for producing chlorine comprise passing an electric current through a brine solution, which decomposes to form chlorine and hydrogen gas and sodium hydroxide (caustic soda).
Various types of electrolytic cells have been developed to accomplish this reaction. Two of the most widely employed types are the mercury cell and the diaphragm cell. In a diaphragm cell, brine is introduced into an anode compartment and flows through a diaphragm into a cathode compartment. Chlorine is formed at the anode and hydrogen and caustic soda at the cathode. The diaphragm prevents the caustic from diffusing into the anode compartment and the two gases are carried away through separate discharge tubes.
Diaphragm type electrolytic cells generally comprise a cover assembly and a base plate upon which the cover assembly rests. The cover assembly with the base plate hermetically encloses the electrolysis zone. A series of spaced anodes are rigidly affixed to the base plate. A series of spaced cathodes is usually rigidly affixed or held within the cover and interleaves or nests with the base assembly anodes when the cover assembly is placed upon the base plate.
The base plate is usually made of copper and is covered by an impermeable cell liner which prevents the electrolytic solution or "anolyte" surrounding the anodes from contacting the base plate. This protection is required because the copper base plate would rapidly be corroded upon exposure to the anolyte solution.
The anodes in a diaphragm type cell are usually attached to the copper base plate by means of stems or rods which are bolted into the base plate and extend through the cell liner to the anodes. The anode stems are often coated with a substance, such as titanium, to resist corrosion. Each stem has a collar which is adapted to be secured against the cell liner to prevent anolyte leakage onto the base plate through the stem holes in the liner.
The cover assembly of the cell is adapted to fit over the base assembly and to form a seal with the cell liner covering the base plate. This seal is often effected by an endless elastomeric rib-like projection extending around the perimeter of the cell liner and which sealably contacts the lower edge of the cover assembly when positioned upon the base plate. This rib-like projection usually is semi-circular in cross-section and is affixed to the cell liner surface by suitable means such as an adhesive.
Because this rib-like sealing member can take a permanent set after a period of time and thereby lose its effectiveness as a seal, the seals are usually changed at prescribed intervals. When changing this seal, however, because the sealing member is affixed to the surface of the liner, the entire liner is replaced.